Direct Measurement of the Spectral Structure of Cosmic-Ray Electrons+Positrons in the TeV Region with CALET on the International Space Station

Abstract

Detailed measurements of the spectral structure of cosmic-ray electrons and positrons from 10.6 GeV to 7.5 TeV are presented from over 7 years of observations with the CALorimetric Electron Telescope (CALET) on the International Space Station. Because of the excellent energy resolution (a few percent above 10 GeV) and the outstanding e/p separation (10${}^5$), CALET provides optimal performance for a detailed search of structures in the energy spectrum. The analysis uses data up to the end of 2022, and the statistics of observed electron candidates has increased more than 3 times since the last publication in 2018. By adopting an updated boosted decision tree analysis, a sufficient proton rejection power up to 7.5 TeV is achieved, with a residual proton contamination less than 10%. The observed energy spectrum becomes gradually harder in the lower energy region from around 30 GeV, consistently with AMS-02, but from 300 to 600 GeV it is considerably softer than the spectra measured by DAMPE and Fermi-LAT. At high energies, the spectrum presents a sharp break around 1 TeV, with a spectral index change from -3.15 to -3.91, and a broken power law fitting the data in the energy range from 30 GeV to 4.8 TeV better than a single power law with 6.9 sigma significance, which is compatible with the DAMPE results. The break is consistent with the expected effects of radiation loss during the propagation from distant sources (except the highest energy bin). We have fitted the spectrum with a model consistent with the positron flux measured by AMS-02 below 1 TeV and interpreted the electron + positron spectrum with possible contributions from pulsars and nearby sources. Above 4.8 TeV, a possible contribution from known nearby supernova remnants, including Vela, is addressed by an event-by-event analysis providing a higher proton-rejection power than a purely statistical analysis.

arXiv commentmain text: 7 pages, 4 figures; supplemental material: 10 pages, 8 figures, 1 table

References in corpus (16)

• Observation of an anomalous positron abundance in the cosmic radiation
• Direct detection of a break in the teraelectronvolt cosmic-ray spectrum of electrons and positrons
• The DArk Matter Particle Explorer mission
• The Most Likely Sources of High Energy Cosmic-Ray Electrons in Supernova Remnants
• Cosmic-ray electron+positron spectrum from 7 GeV to 2 TeV with the Fermi Large Area Telescope
• Extended Measurement of the Cosmic-Ray Electron and Positron Spectrum from 11 GeV to 4.8 TeV with the Calorimetric Electron Telescope on the International Space Station
• Energy Spectrum of Cosmic-ray Electron and Positron from 10 GeV to 3 TeV Observed with the Calorimetric Electron Telescope on the International Space Station
• Electron acceleration in SNR and diffuse gamma-rays above 1 GeV
• Three-Dimensional Model of Cosmic-Ray Lepton Propagation Reproduces Data from the Alpha Magnetic Spectrometer on the International Space Station
• Energy Calibration of CALET Onboard the International Space Station
• On-orbit Operations and Offline Data Processing of CALET onboard the ISS
• Features in cosmic-ray lepton data unveil the properties of nearby cosmic accelerators
• The spectral shapes of the fluxes of electrons and positrons and the average residence time of cosmic rays in the Galaxy
• TeV Electron Spectrum for Probing Cosmic-Ray Escape from a Supernova Remnant
• Implications of a possible TeV break in the cosmic-ray electron and positron flux
• Monte Carlo Study of Electron and Positron Cosmic-Ray Propagation with the CALET Spectrum

Cited by in corpus (5)

• Measurement of Very-high-energy Diffuse Gamma-ray Emissions from the Galactic Plane with LHAASO-WCDA
• High-Statistics Measurement of the Cosmic-Ray Electron Spectrum with H.E.S.S
• Precision spectral measurements of Chromium and Titanium from 10 to 250 GeV$/n$ and sub-Iron to Iron ratio with the Calorimetric Electron Telescope on the ISS
• Transport of electrons in tangled magnetic fields
• Deciphering the Electron Spectral Hardening in AMS-02